Naturalproductman’s Blog

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Archive for the ‘Ring contraction’ Category

This transformation involves making the ring smaller.

Massadine core synthesis

Posted by naturalproductman on October 28, 2015

Daesung Lee and co-workers reported in Organic Letters on the access of the cyclopentane ring core of massadine through a cyclohexane to cyclopentane ring contraction approach by oxidatively cleaving a 1,2-diol intermediate then cyclizing the resulting dialdehyde.
ring

Organic Letters paper

Posted in Alkaloids, Methodology, Ring contraction, Total Synthesis | Leave a Comment »

Ring size matters

Posted by naturalproductman on August 6, 2012

Petr Klan (Masaryk University) and Richard Givens (University of Kansas) have reported in JOC on a study of the photo-Favorskii rearrangement.

ring size

JOC paper

Posted in Cascade Reactions, Favorskii rearrangement, Light Mediated, Methodology, Named Reactions, Ring contraction | Leave a Comment »

Transannular Claisen rearrangement

Posted by naturalproductman on October 23, 2011

Donald Craig and co-workers at Imperial College have reported in Organic and Biomolecular Chemistry on a transannular Claisen rearrangement converting a lactone into a cyclobutane.

Claisen

OBC paper

Posted in Claisen rearrangement, Methodology, Named Reactions, Ring contraction | Leave a Comment »

Bi(OTf)3 mediated rearrangement

Posted by naturalproductman on March 1, 2011

Oliver Reiser and co-workers at Universitat Regensburg in Germany have reported in Organic and Biomolecular Chemistry on a bismuth (III) catalyst that rearranges tricyclic guaianolide rings.

rearrangement

OBC paper

Posted in Cascade Reactions, Mechanistic, Methodology, Ring contraction, Ring expansion, Ring forming, Ring Opening | Leave a Comment »

Vinylogous Amides via Eschenmoser episulfide contractions

Posted by naturalproductman on March 1, 2011

Jan Bergman and co-workers have reported in JOC on an Eschenmoser episulfide contraction reaction to form vinylogous amides.

Eschenmoser

 

JOC paper

Posted in Cascade Reactions, Eschenmoser episulfide contraction, Mechanistic, Methodology, Ring contraction | Leave a Comment »

Ring Contraction via Iodination

Posted by naturalproductman on October 15, 2010

Dias and co-workers at the University of Missouri-Kansas City have published in Chemical Communications on an iodine promoted ring contraction of a C2-symmetric phen-diol.

iodination

 

Chem Comm paper

Posted in Cascade Reactions, Methodology, Ring contraction | Leave a Comment »

6 to 5 Ring Contraction

Posted by naturalproductman on July 5, 2010

Changing a steroid ring from the classical 6,6,6,5-carbon skeleton to a 6,6,5,6-carbon tetracycle can be a challenge, however, it appears to happen in nature with natural products such as cyclopamine and nakiterpiosin.  Athanassios Giannis and co-workers at the Universitat Leipzig in Germany have recently reported in JACS on a way to do such a transformation by using an 11-hydroxy steroid (hydroxy group in only the C-ring adjacent to the axial chiral methyl group)  and subjected to Comin’s reagent (2-[N,N-bis(trifluoromethanesulfonyl)amino]-5-chloropyridine), which is just a triflating agent, and DMAP in toluene under heated conditions to yield the 6 to 5 ring contraction product.

rearrangement

JACS paper

Posted in Cascade Reactions, Comin's, Methodology, Named Reagents, Ring contraction, Steroids | Leave a Comment »

Ring Contraction for Spirocyclic Centers

Posted by naturalproductman on June 21, 2010

Yoshiji Takemoto and co-workers at Kyoto University have published in Chemistry – A European Journal on a ring contraction protocol going from four to three membered rings.

ring contraction

Chemistry A European Journal paper

Posted in Cascade Reactions, Methodology, Ring contraction, Spirocyclic centers | Leave a Comment »

A Ring Contraction Approach for Taiwaniaquinone

Posted by naturalproductman on June 14, 2010

Karl Gademann and co-workers at the University of Basel in Switzerland have published in a ring contraction approach – an intramolecular benzilic acid rearrangement – to access the taiwaniaquinone carbon skeleton.

taiwaniaquinone

Chemistry – a European Journal paper

Posted in Cascade Reactions, Methodology, Ring contraction, Terpenes | Leave a Comment »

Bakkenolide Synthesis

Posted by naturalproductman on April 9, 2010

Luiz Silva and co-workers at the Universidade de Sao Paulo have recently reported in JOC on a ring contraction approach using TTN (thalium III nitrate) to synthesizing the five membered ring in bakkenolide.

ring contraction
JOC paper

Posted in Cascade Reactions, Lactones, Methodology, Ring contraction, Sesquiterpenes | Leave a Comment »